Today Google launched gRPC, a new HTTP/2 and Protocol Buffer based system for building APIs. This is Google's third system for web APIs.
The first system was Google Data, which was based on the Atom Publishing Protocol [RFC 5023]. It was an XML protocol over HTTP. The serving system for that grew, but started to hit scalability issues at around 50 APIs. The scaling issues weren't in the realm of serving QPS, but more in the management of that many APIs, such as rolling out new features across all APIs and all clients.
Those growing pains and lessons learned led to the next generation of APIs that launched in 2010. In addition to writing a whole new serving infrastructure to make launching APIs easier, it was also a time to shed XML and build the protocol on JSON. This Google I/O video contains good overview of the system:
Now, five years later, a third generation API system has been developed, and the team took the opportunity to make another leap, moving to HTTP/2 and Protocol Buffers. This is the first web API system from Google that I haven't been involved in, but I'm glad to see them continuing to push the envelope on web APIs.